The field of the invention generally relates to radio frequency (RF) switches. In one particular embodiment, the invention relates to RF switches and related bypass systems suitable for use in connection with a high temperature superconductor (HTS) based filter and a cryogenically cooled low noise amplifier (LNA).
The increase in the number of mobile telecommunication devices in recent years and the corresponding increase in the amount of data capacity required for such devices has led to the development and implementation of high performance RF filters, including HTS-based RF filters, used in connection with RF front-end devices. HTS filters, for example, are highly selective, low loss filters that substantially decrease interference between adjacent channels.
HTS front-end RF filters require the use of a cryocooler to cool the filters and any associated electronics, such as LNAs, to around 77K. Accordingly, it is preferable that the cryocooler used to cool the filters be able to operate for long periods of time and in a variety of environmental conditions without failing. In some applications, however, a bypass feature is needed in case one or more of the HTS filters contained in the RF front-end fails to perform properly, as would be the case if the cryocooler failed. It is known, for example, td include a bypass feature on a cryogenically cooled receiver front-end that uses two conventional RF relays to bypass the HTS circuitry to direct the antenna signal directly to an output that proceeds to the base station. Because of the high selectivity of the HTS filters the relays used for the bypass function must provide high isolation between poles, typically 50 to 100 dB.
The current bypass systems have a number of limitations. First, the conventional RF relay insertion loss has a relatively high noise figure contribution, which can be 50% or more of the HTS system noise figure. As a result, the potential overall noise figure of the RF receiver is compromised. Consequently, when the system is in bypass state, and/or the LNA is removed, reverse channel, i.e., mobile-to-base, coverage is reduced. Second, conventional RF relays dissipate power in their quiescent or stable state when operated in a fail-safe mode, i.e., if there is a power failure, the relays default to the bypass state. Current relays are also not designed for cryogenic, high vacuum operation. Consequently, conventional RF relays must be located external to the cryogenic enclosure to avoid the relays using up the finite thermal budget of the cryocooler, and to avoid vacuum contamination. Third, the conventional high-isolation, low insertion loss RF relays typically used are rather large devices that increase the overall size and weight of the RF receiver.
Accordingly, there is a need for an improved RF bypass system for a receiver. There is a further need for an improved RF bypass system for an HTS-based filter/LNA RF front-end receiver that has a very low contribution to the noise figure of the overall receiver. There is also a need for a bypass system that provides for very low insertion loss, high isolation, and low intermodulation distortion in both HTS and non-HTS systems. Further, there is a need for a bypass system in which the individual switching elements can be located inside the cryogenic enclosure or other microenclosure of a RF receiver. Placing the switching elements inside the cryogenic enclosure and cooling them may substantially reduce the thermal noise contribution of the switches. Also, the individual switching elements need to have little or no power dissipation when the bypass switches are in their quiescent state to minimize load on the cryocooler.
The present invention provides for improved RF latching switches usable in both HTS and non-HTS receiver systems, and related methods of implementing the latching switches. In one aspect, a RF bypass switch comprises a first switch assembly and a second switch assembly. Each switch assembly, which may be a single throw double throw (SPDT) switch includes an elongate member and a magnet on an end of the elongate member, wherein the magnet is located between a contact pad for a first circuit and a contact pad for a second circuit. The magnet may be oriented such that the direction of the magnetic field is parallel with the length of the elongate member. An electromagnetic field source generates an electromagnetic field that may be perpendicular to the magnet on the elongate member. The electromagnetic field may also be perpendicular to the contact pads of the first circuit and second circuit. The electromagnetic field moves the magnet on the end of the elongate member, either from the first state to the second, or the second state to the first, depending on the polarity of the electromagnetic field. The contact pad for the first and second circuits are made of a ferromagnetic material, such that once the magnet on the end of the elongate member is moved to a contact pad, the magnet on the end of the elongate member is latched to the contact pad by a magnetic force.
The latching switch has a first state and a second state. In the first state, the magnet of each switch assembly is coupled-to the contact pad for the first circuit. In the second state, the magnet of each switch assembly is coupled to the contact pad for the second circuit.
The switch may be transitioned between the first and second states by applying an electromagnetic field from the electromagnetic field source. When in either of the first or second states, the switch may be maintained in that state without further application of a constant electromagnetic field due to the magnetic attraction of the ferromagnetic contact pad.
The electromagnetic field source may include a coil assembly, a lower core, an upper core, and a mid core. The lower core, upper core, and mid core parts are made of a ferromagnetic material, such that the electromagnetic field that is produced can be concentrated and directed in the vicinity of the magnet on the switch. In particular, the electromagnetic field source may be operated to generate an electromagnetic current travelling in a first direction to transition the switch to the first state. When operated to generate an electromagnetic current in the opposite direction, the switch is transitioned to the second state.
A fail safe circuit may be provided. The fail safe circuit may be coupled to the electromagnetic field source. The fail safe circuit provides an electromagnetic discharge to transition the switch between the first and second states. The fail safe circuit may comprise a capacitor or a battery.
Each switch assembly may comprise BeCu or steel. Each switch assembly may also be coupled to a cryocable. A magnet housing may be provided that surrounds each magnet of the switch assemblies.
The first circuit used with the switch may be connected to a HTS circuit, and the second circuit may be a bypass circuit, a transmission line, conventional filter and LNA, or other redundant functional path. When the switch is placed in the first state, the first circuit is operable, and when placed in the second state, the second circuit is operable. Additionally, the switch may include first and second contact points on each switch assembly, wherein the first contact points are configured to couple with the contact pads of the first circuit in the first state, and the second contact points are configured to couple with the contact pads of the second circuit in the second state. The contact pads may be formed from a material such as nickel, steel, and the like.
In another aspect of the present invention, a RF switch comprises a rotor, an elongate member disposed centrally through the rotor, and an actuator assembly coupled to the elongate member and configured to rotate the elongate member. The rotor may be a dielectric rotor. Rotation of the elongate member results in rotation of the rotor. A contact is disposed on a surface of the rotor and is in communication with a substrate. The contact is configured to complete a first path or a second path. In a first state, the contact completes the first path. In a second state, the contact completes the second path. The first path may be, e.g., a HTS circuit, and the second path may be, e.g., a bypass circuit. The contact may be a plurality of contacts disposed on parallel strips. The parallel strips may be on an underside of the rotor. The contact may be formed from BeCu, rhodium and BeCu, steel, or the like. To transition the switch between states, the rotor may be displaced a number of degrees. For a typical rotary switch, for example, the rotor may be displaced 90xc2x0 to transition the bypass switch between the first state and the second state.
The actuator assembly of the bypass switch may include a linear or rotary actuator, a linkage coupled to the linear or rotary actuator, a disk, which may be formed from teflon and aluminum, coupled to the linkage and disposed on an end of the elongate member, a plurality of bearings that may slidably engage a plurality of openings on the lower surface of the disk, and a spring coupled to the elongate member. The spring may compress when the disk is rotated over the bearings, thereby lifting the contact from the surface of the substrate. The disk may comprise teflon and aluminum.
In another aspect of the present invention, a HTS-based RF receiver is provided. The receiver may include a cryogenic enclosure that is in thermal communication with a cryocooler. The receiver may also include a HTS filter. The HTS filter may have an input operatively coupled to a RF input, and an output coupled to a low noise amplifier. The low noise amplifier may have an output coupled to a RF output. Both the HTS filter and the low noise amplifier may be disposed within the cryogenic enclosure. The receiver may also have a bypass system that can operate at both warm and cold temperatures. References to a cold bypass system are intended to refer to a bypass system operable at both warm and cold temperatures. The bypass system comprises a first switch, a second switch, and a bypass circuit disposed between the first switch and the second switch. Each switch may comprise a first and second switch assembly. Each switch assembly may include an elongate member and a magnet on an end of the elongate member. In a bypass state, the magnet is coupled to a contact pad for the bypass circuit. In a HTS state, the magnet is coupled to a contact pad for a circuit connected to a HTS circuit. The HTS circuit is in communication with the HTS filter.
An electromagnetic field source may be coupled to the first and second switch assemblies. Each switch assembly may be transitioned between the HTS state and the bypass state by applying an electromagnetic field from the electromagnetic field source. Also, each switch assembly may be maintained in either the HTS state or the bypass state without a constant application of an electromagnetic field. The bypass system may further include a fail safe circuit coupled to an electronic field source usable to move the magnet on the end of the elongate member between the contact pads of the bypass circuit and the circuit coupled to the HTS circuit. The fail safe circuit provides an electromagnetic discharge to transition each switch assembly between the HTS and bypass states, in the event of a power failure, failure of the electromagnetic field source, or the like. The fail safe circuit may include a capacitor or a battery.
The receiver may incorporate the bypass system within the cryogenic enclosure. In one embodiment, the receiver is mounted atop a tower.
In another aspect of the present invention a HTS-based RF receiver is provided. This receiver may include a cryogenic enclosure in thermal communication with a cryocooler, and a HTS filter having an input operatively coupled to a RF input, and an output coupled with a low noise amplifier. The low noise amplifier may have an output coupled to a RF output. In one embodiment, the HTS filter and the low noise amplifier are disposed within the cryogenic enclosure. A bypass system may be provided that includes first and second switches, a second switch, and a bypass circuit disposed between the first and second bypass switches. Each bypass may include a rotor, an elongate member disposed centrally through the rotor, and an actuator assembly coupled to the elongate member. The rotor may be a dielectric rotor. The actuator assembly rotates the elongate member, which results in rotation of the elongate member.
A contact may be disposed on a surface of the rotor. The contact is in communication with a substrate, and is configured to complete the bypass circuit in a bypass state and to complete a HTS circuit in a HTS state. The HTS circuit is in communication with the HTS filter. The contact may comprise a plurality of contacts disposed on parallel strips.
The bypass system may be disposed within the cryogenic enclosure. In one embodiment, the receiver is mounted atop a tower.
The actuator assembly of the receiver may be used to displace the rotor a certain number of degrees, such as, e.g., 90xc2x0, in order to transition the bypass switch between the HTS and bypass states. The actuator assembly may include a linear or rotary actuator, a linkage coupled to the linear or rotary actuator, a disk, which may include teflon and aluminum, coupled to the linkage and disposed on an end of the elongate member, a plurality of bearings configured to slidably engage a plurality of openings on the lower surface of the disk, and a spring coupled to the elongate member. When the disk is rotated over the bearings, the spring compresses, thereby lifting the contact from the substrate when each bypass switch is transitioned between the HTS and bypass states.
In another aspect of the present invention, a method of operating a RF receiver in a RF filtering active state and a bypass state is provided. The method may include the steps of measuring an operating parameter of the RF receiver, and switching the RF receiver to the bypass state when the measured operating parameter is outside a pre-determined operating range. Switching the RF receiver to the bypass state may be accomplished by applying an electromagnetic field to a switch having a switch assembly comprising an elongate member and a magnet, and terminating application of the electromagnetic field after the magnet of the switch assembly couples with the bypass circuit to complete the bypass circuit around a RF filter.
When the measured operating parameter is within a predetermined range, the method may include switching the RF receiver to the RF filtering active state. Switching the RF receiver to the RF filtering active state may be performed by applying an electromagnetic field to the switch, and terminating application of the electromagnetic field after the magnet of the switch assembly couples with and completes a RF filtering active circuit. The RF filtering active circuit comprises a circuit in communication with a RF filter.
In another aspect of the present invention, another method of operating a RF receiver in a RF filtering active state and a bypass state is provided. This method is performed by measuring an operating parameter of the RF receiver, and switching the RF receiver to the bypass state when the measured operating parameter is outside a pre-determined operating range by applying a force to a switch having a rotor with a contact in communication with a substrate. The substrate is in communication with a bypass circuit and a RF filtering active circuit. The RF filtering active circuit comprises a circuit in communication with a RF filter. The rotor is rotated in order to disrupt the RF filtering active circuit. The rotor is then continued to be rotated until the contact completes the bypass circuit. While rotating the rotor, the contact may be lifted from a surface of the substrate.
When the measured operating parameter is within a predetermined operating range, the receiver may be switched to the RF filtering active state. Switching the receiver to the RF filtering active state may be performed by applying a force to the switch, rotating the rotor to disrupt the bypass circuit, and continuing to rotate the rotor until the contact completes the RF filtering active circuit.
To switch the receiver between the RF filter active circuit and the bypass circuit, applying a force to the switch may be accomplished by using a linear or rotary actuator.
It is an object of the invention to provide a HTS-based RF receiver with a bypass capability. It is another object of the invention to provide a bypass solution that reduces the overall size of the device, regardless of whether the device is HTS or non-HTS.
It is yet another object of the invention to provide a low insertion loss bypass system that is used with HTS-based RF receivers. It is also an object of the invention to provide high performance RF switches usable with both HTS and non-HTS receivers.